PROJECT SUMMARY In rheumatoid arthritis (RA), the cytokine tumor necrosis factor-? (TNF-?) plays a dominant role in driving synovial hyperplasia and progressive destruction of cartilage and bone. Our preliminary data suggests the extracellular enzyme Sulfatase-2 (Sulf-2) to be a potential mediator (or facilitator) of TNF-? signaling in RA synovial fibroblasts (RASFs). At the cell surface, Sulf-2 cleaves sulfate groups from heparan sulfate proteoglycans (HSPGs), which in turn affects the receptor/ligand binding and subsequent signaling of an array of chemokines, cytokines and growth factors. Interactions between TNF-? and HSPGs are not well defined, and the role of Sulf-2 in TNF-? signaling remains unexplored. We found that inhibition of Sulf-2 in human RASFs with siRNA or a small molecule inhibitor (OKN-007) significantly reduced TNF-?-induced expression of adhesion molecules ICAM-1, VCAM-1 and Cadherin-11, and production of inflammatory mediators IL-6 and IL-8. Transcriptome analysis by RNA sequencing (RNAseq) showed that, compared to a negative control siRNA, knockdown of Sulf-2 significantly reduced TNF-? induction of genes related to adhesion, cell proliferation, and chemokines, while concomitantly increasing expression of bone-protective and anti-inflammatory genes. Pathway analysis of RNASeq results showed that Sulf-2 knockdown in TNF-?-stimulated RASFs significantly altered expression of 48 genes in the top canonical pathway Role of Macrophages, Fibroblasts and Endothelial Cells in Rheumatoid Arthritis. This proposal capitalizes on these novel observations, and the central hypothesis of our study is that Sulf-2 mediates TNF-? signaling to promote synovial hyperplasia, invasion and tissue destruction in RA. As an extracellular enzyme, Sulf-2 is an attractive target for pharmacologic inhibition, and a small molecule inhibitor of Sulf-2 has shown high biosafety in human clinical trials. We aim to elucidate the mechanism of Sulf-2 participation in TNF- ? signaling and investigate the potential therapeutic value of targeting Sulf-2-dependent pathways for the treatment of RA. Studies proposed in Aim 1 will investigate the molecular mechanisms of Sulf-2 modulation of TNF-? signaling pathways and effects on downstream mediators of pathogenesis in human RASFs. In Aim 2 we will test the in vivo effects of pharmacologic inhibition of Sulf-2 in a human TNF-? transgenic mouse model of RA. The success of these studies will reveal a novel molecular mechanism of modulating TNF-? signaling in RASFs by regulating Sulf-2, and validate the safety and effectiveness of a potential new pharmacologic treatment for this common and debilitating disease.